To breed for improved heat tolerance, Dr Shaffer said farmers should look for bulls with a high Balanced Performance Index (BPI) and a Heat Tolerance ABV of greater than 100. He said to use a team of bulls to allow for the lower reliability.

The Heat Tolerance ABV, is expressed as a percentage with a base of 100. An animal with a Heat Tolerance ABV of 105 is 5 per cent more tolerant of hot, humid conditions than average.

Its drop in production will be 5 per cent less than the average. The Heat Tolerance ABV is favourably correlated with fertility and unfavourably with production, but natural genetic variation means there will be some high production animals with greater heat tolerance.

Its reliability is 38 per cent, which is lower than conventional production traits but in line with the newer generation of genomic-only traits.

The reliability of the Heat Tolerance ABV is 38 per cent which is in line with the newer generation of genomic-only traits. Like all new ABVs, reliability is expected to improve with time, as more data becomes available.

Heat tolerance is favourably linked with fertility and unfavourably with production. This means a strong focus on heat tolerance bulls may improve fertility but compromise production.

Ray Kitchen from Carenda Holsteins at Boyanup WA will be looking at the new Heat Tolerance ABV when making breeding decisions for his 400-cow herd.

“We will be avoiding using bulls which have low Heat Tolerance ABVs and will be looking for the bulls that pull together production and heat tolerance.”

Mr Kitchen genotypes females so has the Heat Tolerance ABV data for his herd and can see the impact some sires have had on Heat Tolerance.

“We have used bulls in the herd which clearly combine production and Heat Tolerance traits and they are the types of bulls we will be wanting to use in the future.”

While breeding gives cows a helping hand in hot weather, management will still be critical.

The Kitchen’s property at Boyanup regularly experiences summer spells when the day time temperature exceeds 38 degrees C.

Carenda Holsteins is a family partnership comprising Ray Kitchen, his wife Donna, his brother Mal and his wife Lesley.

The year round calving herd is among Australia’s top 10 for genetic merit for profit as measured by the Balanced Performance Index (BPI),